1. Field of the Invention
The present invention relates to catalytic cracking with catalysts comprising crystalline zeolite aluminosilicates. More particularly, the present invention is concerned with hydroprocessing hydrocarbon feeds containing high concentrations of aromatic compounds followed by catalytic cracking of the hydrofined feeds in the presence of crystalline zeolite aluminosilicate catalysts.
2. Description of the Prior Art
A principal process in the petroleum industry by which high boiling hydrocarbons are converted to lower boiling products, including gasoline, is catalytic cracking. Catalytic cracking is to be distinguished from hydrocracking. Hydrocracking involves hydrogenation at temperatures high enough for cracking to occur, whereas catalytic cracking primarily involves cracking in the absence of hydrogen, thereby preventing significant hydrogenation. A distinctive feature of catalytic cracking is the high octane quality of the gasoline produced, resulting from the presence of high concentrations of branched chain paraffin hydrocarbons and olefin hydrocarbons. Catalytic cracking also yields highly unsaturated C.sub.3 and C.sub.4 fractions, and high concentrations of isobutane.
Improvement in the quality of coker gas oil as a catalytic cracking charge stock is disclosed in U.S. Pat. No. 3,098,029 issued July 16, 1963. Hydrofinishing high nitrogen content hydrocarbons followed by catalytic cracking with zeolite aluminosilicates is disclosed in U.S. Pat. No. 3,506,568 issued April 14, 1970.